PARAMECIUM 47 



the animals come into contact with it, they will give a character- 

 istic 'avoiding reaction.' In such a case an animal first backs 

 off a little way from the unsuitable region, changes the course 

 of direction somewhat, and then moves forward in an endeavor to 

 avoid the source of irritation. If the direction taken accomplishes 

 this, then the animal will continue its course ahead until some other 

 external factor intervenes to bring about a change of direction. If 

 the direction taken again brings the animal into contact with the 

 unfavorable medium, the avoiding reaction is again given, and 

 another course is tried. (W. f. 225.) 



In locomotion, the cilia covering the body of the animal exhibit 

 a beautifully coordinated, beating movement. Their action usu- 

 ally drives the animal forward, but by a reversal of the ciliary 

 action, the animal is able to move backward with equal rapidity. 

 It is obvious, of course, that the movements of all the cilia must 

 be in unison if a definite progression of the animal is to be obtained. 

 It is an interesting problem to determine how the beats of almost 

 innumerable cilia can be controlled in such a way as to bring uni- 

 formity of action, or how the action of all the cilia can be reversed 

 suddenly, and the animal thereby driven in the opposite direction. 

 It would seem as if there must of necessity be some sort of com- 

 plicated controlling mechanism to bring about such coordination, 

 and, as a matter of fact, evidence has recently been found in several 

 species of Ciliates, including Paramecium, which indicates that a 

 coordinating 'neuromotor' apparatus of differentiated cytoplasm 

 is present. Presumably this apparatus functions somewhat like 

 the nervous system in the higher forms of animals. (W. f. 135.) 



TEXTBOOK REFERENCES 

 Woodruff, pp. 43-45 ; 53-56 ; 255-260 ; 343-348. 



Curtis and Guthrie, pp. 175-190 ; 202-212 ; 559. 

 Guyer, pp. 191-197; 664-665. 

 Hegner, pp. 51-71. 

 Newman, pp. 96 ; 129-145. 

 Shull, pp. 84 ; 251 ; 149-150. 



GENERAL REFERENCES 



Calkins. Biology of the Protozoa (Lea and Febriger). 



Hartog. " Protozoa," in the Cambridge Natural History (Macmillan). 



Kudo. Handbook of Protozoology (Thomas). 



Parker and Haswell. Textbook of Zoology (Macmillan). 



